Submersible pump

ABSTRACT

A submersible pump includes a fluid-end section, a power-end section, a top connection sub and an umbilical. The fluid-end section includes a tubular fluid-end barrel, an upper piston disposed within the fluid-end barrel bore, and a traveling valve disposed at the upper piston upper end. The power-end section includes a tubular hydraulic cylinder. A lower piston disposed within the hydraulic cylinder bore is connected to the upper piston. The top connection sub connected to the fluid-end barrel upper end has a discharge port and a standing valve disposed below the discharge port. The umbilical includes first and second tubing strings providing fluid communications between a prime mover and the hydraulic cylinder bore below and above the lower piston face, respectively. A third tubing string provides fluid communications between a wellhead and the top connection sub discharge port.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application Ser. No. 61/769,970 filed Feb. 27, 2013.

BACKGROUND

The invention relates to an apparatus for recovering fluids, particularly hydrocarbons, from subterranean wells, including substantially vertical wells, deviated wells, and substantially horizontal wells. More specifically, the invention relates to an inline hydraulic reciprocating submersible pump.

SUMMARY

There is provided a submersible pump for use with a downhole well having a wellhead, a prime mover providing wellbore fluid, and a wellbore extending from the wellhead. The pump comprises an upper, fluid-end section; a lower, power-end section; a top connection sub; a ported suction strainer and an umbilical. The fluid-end section includes a tubular fluid-end barrel having an axially extending bore. An axially, slidably movable upper piston is disposed within the fluid-end barrel bore. The upper piston has upper and lower ends and a bore extending axially from the upper end. A traveling valve is disposed at the upper piston upper end. The upper piston bore is in fluid communication with a space above the upper piston when the traveling valve is in the open position and no fluid can flow between the upper piston bore and the space above the upper piston when the traveling valve is in the closed position. The power-end section includes a tubular hydraulic cylinder having upper and lower ends and an axially extending bore. An axially, slidably movable lower piston is disposed within the hydraulic cylinder bore. The lower piston is connected to the upper piston lower end and has upper and lower piston faces. The top connection sub is connected to the fluid-end barrel upper end and has a discharge port and a standing valve disposed below the discharge port. The space above the upper piston is in fluid communication with the discharge port when the standing valve is in the open position and no fluid can flow between the space above the upper piston and the discharge port when the standing valve is in the closed position. The suction strainer is disposed intermediate the fluid-end section and the power-end section and has an axially extending bore. The umbilical includes a first tubing string providing fluid communications between the prime mover and the hydraulic cylinder bore below the lower piston face; a second tubing string providing fluid communications between the prime mover and the hydraulic cylinder bore above the upper piston face; and a third tubing string providing fluid communications between the wellhead and the top connection sub discharge port.

The upper piston bore extends axially from the upper end and the upper piston also includes a ported piston rod adaptor disposed at the lower end. The piston rod adaptor has a fluid passage for flow of wellbore fluid into the upper piston bore.

The lower piston is connected to the upper piston lower end by a connecting rod that extends upwardly from the upper piston face to an upper end connected to upper piston lower end.

The submersible pump may further comprise a bottom connection sub connected to the hydraulic cylinder lower end. The bottom connection sub has a port connectable to first tubing string.

The submersible pump may further comprise an intermediate connection sub disposed intermediate the suction strainer and the power-end section. The intermediate connection sub includes a lower end connected to the hydraulic cylinder upper end, a port connectable to the second tubing string, and an axially extending bore.

The suction strainer may include a lower end connected to the intermediate connection sub, and an upper end connected to the fluid-end barrel lower end.

The intermediate connection sub may also have an upper end connected to the suction strainer lower end, the intermediate connection sub upper end comprising a seal section. The seal section may have an axially extending bore.

The lower piston connecting rod may have an axially extending bore for directing a portion of the wellbore fluid from the lower piston into the fluid-end barrel whereby the upper piston is lubricated.

The lower piston has an outer surface that engages the hydraulic cylinder inner surface forming a fluid seal between the hydraulic cylinder bore below the lower piston face and the hydraulic cylinder bore above the upper piston face.

The submersible pump may further comprising a pressure sensor disposed in the hydraulic cylinder that sends pressure signals to a controller of the prime mover.

The standing valve and the traveling valve may each include a spring, a stem guide, a valve body and a seat, the spring and the stem guide directing the valve body to engage the seat.

BRIEF DESCRIPTION OF THE DRAWINGS

Drawings are included for the purpose of illustrating certain aspects of the invention. Such drawings and the description thereof are intended to facilitate understanding and should not be considered limiting of the invention. Drawings are included, in which:

FIG. 1 is an elevation view of one embodiment of an apparatus of the present invention;

FIG. 2 is a cross-sectional view of the apparatus in FIG. 1, along line C-C;

FIG. 3 is an elevation view of one embodiment of a piston assembly for use with the apparatus of the present invention; and

FIG. 4 is a cross-sectional view of the piston assembly in FIG. 3, along line D-D.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments contemplated by the inventor. The detailed description includes specific details for the purpose of providing a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.

Referring to FIGS. 1 to 4, an apparatus 10 for recovering fluids, especially hydrocarbons, from a subterranean well is provided. The apparatus illustrated in FIGS. 1 and 2 may not be drawn to scale. In this disclosure, “upper” or “above” generally denotes a position that is closer to the well opening at the surface than “lower” or “below,” when the apparatus is situated downhole.

The apparatus generally comprises two sections: a lower section (also sometimes referred to as the drive section or power-end); and an upper section (also sometimes referred to as the driven section or fluid-end). The apparatus is for deployment into the wellbore using a round, coiled tubing umbilical and a standard coiled tubing service unit. The coiled umbilical comprises three small diameter tubing strings that are consolidated within a high density encapsulation material. In one embodiment, the tubing strings are made of stainless steel and the encapsulation material is polyethylene. Two of the tubing strings 12, 13 within the umbilical are for providing hydraulic force from a prime mover at surface to the power-end section of the apparatus, and the third tubing string 14 is for transporting pumped fluid from the fluid-end section of the apparatus to a wellhead at surface.

The apparatus further comprises a middle connection sub 16, which separates the power-end from the fluid-end of the apparatus. The power-end includes a hydraulic cylinder 18, which is a tubular member having an inner surface that defines an axially extending bore. The hydraulic cylinder houses a lower piston 20 that is slideably movable axially inside its bore. Lower piston 20 has an upper piston face and a lower piston face. Lower piston 20 engages the inner surface of the hydraulic cylinder such that it provides a fluid seal between the space adjacent to the lower piston face and the space adjacent to the upper piston face.

The fluid-end includes a fluid-end barrel 22, which is a tubular member having an inner surface that defines an axially extending bore. The fluid-end barrel houses an upper piston 24 that is slideably movable axially inside its bore. Upper piston 24 inside the fluid-end barrel is a tubular member having an inner surface defining an axially extending bore. Piston 24 includes a ported piston rod adaptor 36 at its lower end, which provides a fluid passage for wellbore fluid to flow into the bore of the piston 24. A travelling valve 38 (sometimes referred to as a suction valve) is provided at an upper end of the piston 24. When travelling valve 38 is open, the inner bore of piston 24 is in fluid communication with the space above the piston inside the fluid-end barrel 22. When travelling valve 38 is closed, no fluid can flow between the inner bore of piston 24 and the space above the piston inside the fluid-end barrel 22.

An upper end of the hydraulic cylinder 18 is connected to a lower end of the middle connection sub. The middle connection sub includes a seal section 26 at its upper end which is connected to a lower end of a ported suction strainer 28. The middle connection sub, the seal section, and the ported suction strainer each have an axial bore extending therethrough, and the long axes of these three bores substantially align with one another. An upper end of the ported suction strainer is connected to a lower end of the fluid-end barrel. A lower end of the hydraulic cylinder is connected to a bottom connection sub 30. An upper end of the fluid-end barrel is connected to a top connection sub 32.

The top connection sub 32 includes a standing valve 40 (sometimes referred to as a discharge valve). A discharge port provided above the standing valve is connectable to the tubing string 14 of the umbilical to allow the flow of wellbore fluid up the tubing string 14 to the wellhead at surface. When standing valve 40 is open, fluid in the space above piston 24 inside fluid-end barrel 22 can flow out of the discharge port and into the tubing string 14. When standing valve 40 is closed, no fluid can flow out of the discharge port.

The upper piston face of lower piston 20 is connected to a lower end of the upper piston 24 by a connecting rod 34. The connecting rod extends through the bore of the seal section. The seal section keeps the high pressure drive oil in the power-end separated from the wellbore fluid in the fluid-end. The ported suction strainer allows wellbore fluid to flow into the fluid-end barrel during the operation of the apparatus, while screening out particulates in the wellbore fluid that are greater than a certain size.

The tubing strings 12 and 13 are for supplying high pressure drive fluid to the power-end of the apparatus. Tubing strings 12 and 13 are connected to and are in fluid communication with the bottom connection sub and the middle connection sub, respectively. The bottom connection sub and middle connection sub are internally ported to deliver the high pressure drive fluid below the lower piston face and above the upper piston face of lower piston 20. Alternating the supply of drive fluid in the two tubing strings 12, 13 moves the lower piston up and down, which will be described in more detail hereinbelow.

As lower piston 20 in the power-end is driven in one direction by the supply of drive fluid from the prime mover at surface, a force is applied to upper piston 24 by the connecting rod, thereby creating the reciprocating action of the upper piston which allows the apparatus to operate.

In one embodiment, the components of the apparatus 10 are connected to one another by threaded connections; however, other methods of connecting the components may be possible. In a further embodiment, the components of the apparatus 10 are made of stainless steel; however, other materials that can withstand wellbore conditions, such as high temperatures and high pressures, may also be used.

In operation, apparatus 10 is typically deployed into the wellbore on round umbilical coiled tubing which is suspended from the wellhead using standard coiled tubing hanger equipment. The apparatus is installed at a depth below the producing perforations in the wellbore where produced fluid is allowed to accumulate within the casing of the well.

At the wellhead, tubing strings 12 and 13 are connected to drive fluid lines from the prime mover and tubing string 14 is connected to pipe lines for transporting the pumped wellbore fluid. With the prime mover running and engaged, high pressure drive fluid is pumped down one of the tubing strings 12, 13 into the space adjacent to one piston face of lower piston 20. As fluid pressure increases in the space adjacent to the one piston face of lower piston 20, lower piston 20 moves axially within hydraulic cylinder 18 in one direction and any fluid in the space adjacent to the other piston face of lower piston 20 is pushed out of the hydraulic cylinder 18 through the corresponding tubing string 12, 13. Since lower piston 20 is connected to upper piston 24 via the connecting rod 34, the movement of lower piston 20 in one direction drives upper piston 24 in the same direction.

The prime mover at surface has a directional controller for sensing pressure spikes of the drive fluid. When upper piston 24 reaches the end of its travel in fluid-end barrel 22, lower piston 20 cannot move any further in the one direction and fluid pressure quickly increases inside hydraulic cylinder 18 as one of the tubing strings 12, 13 continues to supply drive fluid to the one side of lower piston 20. Once the directional controller senses a sharp pressure spike of the drive fluid, the controller shifts the high pressure drive fluid to the other tubing string 12, 13, thereby pushing the lower piston to move in the opposite direction inside hydraulic cylinder 18. The movement of lower piston 20 also moves upper piston 24 in the same direction. This operation of reciprocating the motion of lower piston 20 repeats automatically until the prime mover is shut down. The reciprocating motion of lower piston 20 causes upper piston 24 to reciprocate in the same manner.

The speed of the apparatus (i.e. number of piston strokes per minute) is controlled by adjusting the volume of drive fluid at the prime mover. In most applications, the speed of the apparatus is adjusted to substantially match the inflow rate of the produced fluid to help ensure that there is fluid in the wellbore for the apparatus to lift to surface.

As piston 24 travels downward, a vacuum (or negative pressure) is created in the fluid-end barrel above the piston 24, thereby opening travelling valve 38. The vacuum, as well as the hydrostatic weight of the column of fluid in the wellbore, causes the wellbore fluid to flow through the ported suction strainer 28, through the ported piston rod adaptor 36, through the inner bore of piston 24 and the opened traveling valve 38 and into the space above the piston 24 inside the fluid-end barrel 22. As a result, as the piston 24 moves from the upper end to the lower end of the fluid-end barrel, some of the wellbore fluid is drawn into the apparatus to fill the inner bore of the fluid-end barrel above the piston 24. The downward movement of piston 24 and the corresponding filling of the fluid-end barrel are referred to as the suction stroke.

Once piston 24 reaches the lower end of fluid-end barrel, the drive fluid supply is switched from tubing string 13 to tubing string 12, thereby pumping drive fluid into the space adjacent to the lower piston face of piston 20 and consequently reversing the direction of movement of piston 24. When the piston 24 moves upward and begins the discharge stroke, the fluid pressure in the space above piston 24 inside the fluid-end barrel increases and this increase in pressure forces travelling valve 38 to close and standing valve 40 to open. As piston 24 continues to move upwards towards the upper end of the fluid-end barrel, the fluid that filled the inside of the fluid-end barrel during the suction stroke is forced out of fluid-end barrel 22 through the opened standing valve 40 and the discharge port into tubing string 14. The upward movement of piston 24 and the corresponding emptying of the fluid-end barrel are referred to as the discharge stroke.

The repetition of the suction stroke and the discharge stroke causes fluid in the wellbore to be pumped up tubing string 14 to the wellhead at surface.

In one embodiment, when the apparatus is for use in a horizontal section of a wellbore, the standing valve 40 and the travelling valve 38 further include a spring and stem guide to help direct the valve to the seat.

In a further embodiment, the connecting rod 34 has an axially extending bore therein for directing some of the drive fluid from either side of lower piston 20 to flow into fluid-end barrel 22 to lubricate upper piston 24. More specifically, an oil galley is provided between the inner surface and outer surface of upper piston 24 and an opposing seal set is disposed between the outer surface of piston 24 and the inner tubular wall of the fluid-end barrel. The drive fluid may be selected for its lubrication value as required for a particular pumping application.

Having the suction inlet (i.e. ported suction strainer 28) at or near the lower end of fluid-end barrel 22 creates some back-flow of the wellbore fluid. More specifically, as piston 24 travels down the barrel during the suction stroke, and before it reverses direction to begin the discharge stroke, some of the fluid below piston 24 is forced out of the apparatus through ported suction strainer 28 and back into the wellbore, thereby creating a back-flush flow that may help dislodge any buildup of solids on the outer surface of the ported suction strainer.

Apparatus 10 is configured to allow substantially all of the fluid above piston 24 in fluid-end barrel 22 to be pushed out of the apparatus at the end of the discharge stroke. Having the travelling valve positioned below the standing valve in the apparatus may assist in the discharging of fluid-end barrel 22 of substantially all fluids therein. The configuration of apparatus 10, particularly the location of the travelling valve relative to the standing valve, may minimize the possibility of gas locking the apparatus.

Apparatus 10 does not have to be driven by hydraulics. Apparatus 10 may be modified for use with a rod pump or electric submersible pump, while maintaining the relative positions of the valves (i.e. the travelling valve being positioned below the standing valve).

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to those embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the full scope consistent with the claims, wherein reference to an element in the singular, such as by use of the article “a” or “an” is not intended to mean “one and only one” unless specifically so stated, but rather “one or more”. All structural and functional equivalents to the elements of the various embodiments described throughout the disclosure that are known or later come to be known to those of ordinary skill in the art are intended to be encompassed by the elements of the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. For US patent properties, it is noted that no claim element is to be construed under the provisions of 35 USC 112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or “step for”. 

What is claimed is:
 1. A submersible pump adapted for use with a downhole well having a wellhead, a prime mover providing wellbore fluid, and a wellbore extending from the wellhead, the pump comprising: an umbilical including a first tubing string adapted to provide fluid communications with the prime mover, a second tubing string adapted to provide fluid communications with the prime mover, and a third tubing string adapted to provide fluid communications with the wellhead; an upper, fluid-end section including a tubular fluid-end barrel extending from an upper end to a lower end and having an inner surface that defines an axially extending bore, and an upper piston disposed within the fluid-end barrel bore and axially, slidably movable therein, the upper piston extending from an upper end to a lower end and having an inner surface defining a bore extending axially from the upper end, a ported piston rod adaptor disposed at the lower end defining a fluid passage for flow of wellbore fluid into the upper piston bore, and a traveling valve disposed at the upper piston upper end, the traveling valve having open and closed positions wherein the upper piston bore is in fluid communication with a space above the upper piston when the traveling valve is in the open position and no fluid can flow between the upper piston bore and the space above the upper piston when the traveling valve is in the closed position; a lower, power-end section including a tubular hydraulic cylinder extending from an upper end to a lower end and having an inner surface defining an axially extending bore, and a lower piston disposed within the hydraulic cylinder bore and axially, slidably movable therein, the lower piston having an upper piston face, a connecting rod extending upwardly from the upper piston face to an upper end connected to upper piston lower end, and a lower piston face; a top connection sub connected to the fluid-end barrel upper end having a discharge port connectable with the third tubing string, and a standing valve disposed below the discharge port, the standing valve having open and closed positions wherein the space above the upper piston is in fluid communication with the discharge port when the standing valve is in the open position and no fluid can flow between the space above the upper piston and the discharge port when the standing valve is in the closed position; a bottom connection sub connected to the hydraulic cylinder lower end, the bottom connection sub having a port connectable to first tubing string providing fluid communication with the hydraulic cylinder bore below the lower piston face; an intermediate connection sub having a lower end connected to the hydraulic cylinder upper end, a port connectable to second tubing string providing fluid communication with the hydraulic cylinder bore above the upper piston face, and an inner surface defining an axially extending bore; and a ported suction strainer having a lower end connected to the intermediate connection sub, an upper end connected to the fluid-end barrel lower end, and an inner surface defining an axially extending bore.
 2. The submersible pump of claim 1 wherein the intermediate connection sub also has an upper end connected to the ported suction strainer lower end, the intermediate connection sub upper end comprising a seal section.
 3. The submersible pump of claim 2 wherein the seal section has an inner surface defining an axially extending bore.
 4. The submersible pump of claim 1 wherein the lower piston connecting rod defines an axially extending bore for directing a portion of the wellbore fluid from the lower piston into the fluid-end barrel whereby the upper piston is lubricated.
 5. The submersible pump of claim 1 wherein the lower piston has an outer surface that engages the hydraulic cylinder inner surface defining a fluid seal between the hydraulic cylinder bore below the lower piston face and the hydraulic cylinder bore above the upper piston face.
 6. The submersible pump of claim 1 further comprising a pressure sensor disposed in the hydraulic cylinder, the pressure sensor being adapted to send pressure signals to a controller of the prime mover.
 7. The submersible pump of claim 1 wherein the standing valve and the traveling valve each include a spring, a stem guide, a valve body and a seat, the spring and the stem guide directing the valve body to engage the seat.
 8. A pumping system adapted for use with a downhole well having a wellhead and a wellbore extending from the wellhead, the pumping system comprising: a prime mover providing a high pressure wellbore fluid; a submersible pump comprising an upper, fluid-end section including a tubular fluid-end barrel extending from an upper end to a lower end and having an inner surface that defines an axially extending bore, an upper piston disposed within the fluid-end barrel bore and axially, slidably movable therein, the upper piston extending from an upper end to a lower end and defining a bore extending axially from the upper end, and a traveling valve disposed at the upper piston upper end, the traveling valve having open and closed positions wherein the upper piston bore is in fluid communication with a space above the upper piston when the traveling valve is in the open position and no fluid can flow between the upper piston bore and the space above the upper piston when the traveling valve is in the closed position, a lower, power-end section including a tubular hydraulic cylinder extending from an upper end to a lower end and having an inner surface defining an axially extending bore, and a lower piston disposed within the hydraulic cylinder bore and axially, slidably movable therein, the lower piston being connected to the upper piston lower end and having an upper piston face, and a lower piston face, a top connection sub connected to the fluid-end barrel upper end having a discharge port, and a standing valve disposed below the discharge port, the standing valve having open and closed positions wherein the space above the upper piston is in fluid communication with the discharge port when the standing valve is in the open position and no fluid can flow between the space above the upper piston and the discharge port when the standing valve is in the closed position, and a ported suction strainer disposed intermediate the fluid-end section and the power-end section, the strainer defining an axially extending bore; and an umbilical including a first tubing string providing fluid communications between the prime mover and the hydraulic cylinder bore below the lower piston face, a second tubing string providing fluid communications between the prime mover and the hydraulic cylinder bore above the upper piston face, and a third tubing string providing fluid communications between the wellhead and the top connection sub discharge port.
 9. The submersible pump of claim 8 wherein the submersible pump further comprises a pressure sensor disposed in the hydraulic cylinder, and the prime mover includes a directional controller in communication with the submersible pump pressure sensor, the directional controller being adapted to sense pressure spikes of the wellbore fluid.
 10. The submersible pump of claim 9 wherein the directional controller shifts the high pressure wellbore fluid to another of the first or second tubing strings when a pressure spike of the wellbore fluid is sensed.
 11. The submersible pump of claim 9 wherein the submersible pump has a speed of operation, the wellbore fluid has a flow volume, and the directional controller controls the submersible pump speed of operation by adjusting the wellbore flow volume.
 12. A submersible pump adapted for use with a downhole well having a wellhead, a prime mover providing wellbore fluid, and a wellbore extending from the wellhead, the pump comprising: an upper, fluid-end section including a tubular fluid-end barrel extending from an upper end to a lower end and having an inner surface that defines an axially extending bore, an upper piston disposed within the fluid-end barrel bore and axially, slidably movable therein, the upper piston extending from an upper end to a lower end and defining a bore extending axially from the upper end, and a traveling valve disposed at the upper piston upper end, the traveling valve having open and closed positions wherein the upper piston bore is in fluid communication with a space above the upper piston when the traveling valve is in the open position and no fluid can flow between the upper piston bore and the space above the upper piston when the traveling valve is in the closed position, a lower, power-end section including a tubular hydraulic cylinder extending from an upper end to a lower end and having an inner surface defining an axially extending bore, and a lower piston disposed within the hydraulic cylinder bore and axially, slidably movable therein, the lower piston being connected to the upper piston lower end and having an upper piston face, and a lower piston face, a top connection sub connected to the fluid-end barrel upper end having a discharge port, and a standing valve disposed below the discharge port, the standing valve having open and closed positions wherein the space above the upper piston is in fluid communication with the discharge port when the standing valve is in the open position and no fluid can flow between the space above the upper piston and the discharge port when the standing valve is in the closed position; a ported suction strainer disposed intermediate the fluid-end section and the power-end section, the strainer defining an axially extending bore; and an umbilical including a first tubing string adapted to provide fluid communications between the prime mover and the hydraulic cylinder bore below the lower piston face, a second tubing string adapted to provide fluid communications between the prime mover and the hydraulic cylinder bore above the upper piston face, and a third tubing string adapted to provide fluid communications between the wellhead and the top connection sub discharge port.
 13. The submersible pump of claim 12 wherein the upper piston bore extends axially from the upper end and the upper piston also includes a ported piston rod adaptor disposed at the lower end, the piston rod adaptor defining a fluid passage for flow of wellbore fluid into the upper piston bore.
 14. The submersible pump of claim 12 wherein the lower piston is connected to the upper piston lower end by a connecting rod, the connecting rod extending upwardly from the upper piston face to an upper end connected to upper piston lower end.
 15. The submersible pump of claim 12 further comprising a bottom connection sub connected to the hydraulic cylinder lower end, the bottom connection sub having a port connectable to first tubing string.
 16. The submersible pump of claim 12 further comprising an intermediate connection sub disposed intermediate the suction strainer and the power-end section, the intermediate connection sub including a lower end connected to the hydraulic cylinder upper end, a port connectable to the second tubing string, and an inner surface defining an axially extending bore.
 17. The submersible pump of claim 16 wherein the suction strainer includes a lower end connected to the intermediate connection sub, and an upper end connected to the fluid-end barrel lower end.
 18. The submersible pump of claim 12 wherein the intermediate connection sub also has an upper end connected to the suction strainer lower end, the intermediate connection sub upper end comprising a seal section.
 19. The submersible pump of claim 18 wherein the seal section has an inner surface defining an axially extending bore.
 20. The submersible pump of claim 12 wherein the lower piston connecting rod defines an axially extending bore for directing a portion of the wellbore fluid from the lower piston into the fluid-end barrel whereby the upper piston is lubricated.
 21. The submersible pump of claim 12 wherein the lower piston has an outer surface that engages the hydraulic cylinder inner surface defining a fluid seal between the hydraulic cylinder bore below the lower piston face and the hydraulic cylinder bore above the upper piston face.
 22. The submersible pump of claim 12 further comprising a pressure sensor disposed in the hydraulic cylinder, the pressure sensor being adapted to send pressure signals to a controller of the prime mover.
 23. The submersible pump of claim 12 wherein the standing valve and the traveling valve each include a spring, a stem guide, a valve body and a seat, the spring and the stem guide directing the valve body to engage the seat. 